This invention concerns improvements in or relating to seat suspension arrangements of the kind enabling the contour of the support provided by a seat to be adjusted by the user. The arrangement is particularly intended for use in the backrest of a vehicle seat to provide adjustable lumbar support, but it will be appreciated that the principle may be applied to any other arrangement wherein the contour of a seat cushion is desired to be adjusted, for example to a seat base having means for providing adjustable thigh support.
The present invention has particular reference to a seat suspension arrangement of the kind described and claimed in our co-pending International Patent Application No PCT/EP97/04580 (Publication No WO 98/07590) the contents of which are included herein by this reference. The invention is not limited to application in this context, however.
Arrangements of the kind referred to above are applicable to seats having upholstery supporting means suspended transversely in the seat to support the seat upholstery, and make use of tensioning elements in the form of one or more adjustable links that can serve to vary the degree of tension in the upholstery supporting means suspended in the seat frame in a given region, for example the lumbar region, to cause variation in the profile of the upholstery support. The adjustable links are advantageously provided by Bowden cables.
When such an arrangement is applied to a seat back to provide adjustable lumbar support, it gives lumbar adjustment in a horizontal direction. However there is an increasing demand for vehicle seats with so-called xe2x80x9cfour wayxe2x80x9d lumbar adjustment in which the lumbar supporting area of the seat can be moved to and fro, not only in the horizontal direction, but also vertically.
The additional vertical adjustment has been provided in some known arrangements by arranging for vertical movement of the upholstery supporting means itself as a unit in order to move the point of lumbar support. However such an arrangement is relatively complicated and expensive and would in any case be very difficult to apply to a Bowden cable actuated mechanism of the kind under consideration.
It is therefore an object of the invention to provide an improved arrangement of the kind using tensioning elements in the form of adjustable links to adjust the contour of a seat support in which more versatile adjustment of the contour of such a platform element is possible.
According to the invention there is provided a seat arrangement comprising a seat frame, upholstery supporting means suspended transversely between lateral margins of the seat frame and adjustable link means for varying the tranverse tension in the upholstery supporting means between said margins at a given point in order to vary the effective profile of the support provided by said supporting means, wherein a plurality of said adjustable link means are provided, spaced apart in a direction parallel to said margins of the seat frame, and means is provided for enabling adjustment of the relative lengths of said plurality of link means in such a manner that the profile of the support can be varied, both to adjust the degree of support provided at a given point, and also to adjust the position of the point at which said support is provided.
A preferred embodiment of the present invention comprises a seat frame and a platform element adapted to provide support for upholstery of the seat, the platform element being linked to the seat frame by adjustable link means disposed at two or more locations along at least one margin of the platform element, the said platform element being so constructed that it is resiliently extensible in a direction towards said margin of said seat frame, means being provided for adjusting the effective length of said link means, the arrangement being such that with the link means in an extended condition at at least one of the said two or more locations on the margin of the platform element at least one portion thereof is recessed relatively to a boundary of the seat frame forming an attachment for the link means, and said adjustable link means being supplemented by further non-adjustable link means for retaining the position of the margin of said platform element relatively to the seat frame whereby upon contraction of the adjustable link means said portion of the platform element is displaced towards said boundary in order to vary the contour of the said platform element.
The adjustable link means may conveniently be provided for each side margin of the platform element at at least two locations on each said side margin.
The adjustable link means for the or each margin may be provided with a separate mounting bracket at each location or may be provided with a common mounting bracket spanning the locations at each margin.
Advantageously the means for adjusting the effective length of the adjustable link means are formed of Bowden cables suitably mounted in the brackets referred to above and may be manually actuable or in the alternative may be actuated by one or more suitable power packs controllable by the seat user according to personal preference.